from http://www.apple.com/macosx/leopard/timemachine.html
Preferential Treatment
Time Machine works great out of the box, but you can customize it by modifying the following behaviors in System Preferences:
* Backup Disk: Change the drive or volume you’re backing up to. Or back up to a Mac OS X server computer.
* Do Not Backup: By default, Time Machine backs up your entire system. But you can also select items you’d rather not back up.
* Backup Time: Time...